The invention relates to a soot-particle filter arranged in the exhaust-line system of an internal-combustion engine of the type having a bypass line guiding the exhaust-gas stream past the soot-particle filter and closable under the full load of the internal-combustion engine.
German Published Unexamined Patent Application (DOS) 3,235,953 makes known a soot-particle filter of the relevent generic type which is subjected to the exhaust gas only when the internal-combustion engine is operating under full load.
In contrast, in other load ranges, the exhaust gas laden with soot particles is guided past the filter through a bypass line and cleaned via a separate soot-particle separator device. A disadvantage of this arrangement is that, when the soot-particle filter is clogged, in those operating ranges in which the exhaust-gas temperatures necessary for the regeneration of the filter do not apply, the internal-combustion engine cannot be operated under full load during the start-up process and, in general, during acceleration out of low speed ranges, since because the bypass line is generally closed under full load there is a very rapid and sharp increase in the exhaust-gas back-pressure and consequently, under certain circumstances, the internal-combustion engine stops.
If the filter is not blocked completely, although it is unlikely that the internal-combustion engine will stop immediately, nevertheless, under full-load conditions, a stationary state is established even in the lowest speed ranges, with such an excessively high exhaust-gas back-pressure that the quantity of fuel injected is converted into soot particles to an increased extent because of a corresponding lack of air and an impaired mixture formation, and therefore the time elapsing until the soot-particle filter is clogged completely is only very short.
An object on which the invention is based is, therefore, to develop further a soot-particle filter arrangement in the exhaust-line system of an internal-combustion engine of the type described above, in such a way that, when the filter is almost or completely clogged, a start-up or an acceleration out of low speed ranges is generally possible under full-load conditions, that is to say even when the exhaust-gas temperature is of a value insufficient for the regeneration of the filter.
According to preferred embodiments of the invention, this object is achieved by an arrangement wherein the bypass line is opened only when (i) the speed of the internal-combustion engine is below a first speed limit value during its warm-up phase, (ii) the speed of the internal-combustion engine is below a second speed limit value under hot-running conditions, and, (iii) with the soot-particle filter laden, the internal-combustion engine load is simultaneously below a predetermined load limit.
Since the bypass line is opened in the lower speed ranges during the warm-up phase, and also when the internal-combustion engine is already running hot, there is no possibility of a critical increase in the exhaust-gas back-pressure, thus ensuring an easy and smooth start-up and acceleration in these ranges, even under full-load conditions. At higher internal-combustion engine speeds, the soot-particle filter is subject to charging when it is still sufficiently capable of receiving soot particles, that is to say when a predetermined limiting exhaust-gas back-pressure has not yet been reached. At an exhaust-gas pressure which is above this limiting value, the soot filter is charged only when there is a guarantee that the exhaust gas is at a temperature sufficient for the regeneration of the filter, that is to say above a predetermined load limit value. It is therefore impossible, in any operating state, for the internal-combustion engine to stop as a result of a blocked filter. Even starting the internal-combustion engine with the soot filter completely clogged presents no difficulties of any kind.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.